What you read was wrong and is fucking opposite from reality, a "partner" nation to Apollo would be expected to provide huge ass funding, and any "partner" would not be responsible for ANYTHING on the critical path to landing on the moon. It was an American program, if a partner nation got on board the MOST they could expect was experiments flying (and wouldn't be a priority either)
Nixon was recorded asking a random thought he had of internationalizing Shuttle. It was shot down fast due to it entailing the US to give up cutting edge technology for a little bit of money. And it would essentially make the program unkillable. NASA partnerships for shuttle were mostly science package related, like spacelab and stuff, not anything on the vehicle itself
To begin with, I fear I have not been clear in my usage of "International Apollo". As my brain keeps lumping in all of the Apollo-necessitated space science programs -- e.g. Ranger and especially Surveyor -- into Apollo. Which, as a matter of terminology, is not strictly true. When I have spoken of "International Apollo", I've not meant participation in the actual Apollo program, because no one was able to pay to move at the speed NASA wanted and, even if somebody had been, it's unlikely NASA would have wanted to make itself reliant on anyone else. What I've meant is participation in that wide set of space science programs through complementary national missions.
Returning to what was actually typed, isn't that mostly the point I was making? "International Apollo" would be a repeat of the Shuttle's international component, where NASA initially welcomed international "partners" whose job was to give them money to build what NASA wanted in the way NASA chose to, and be grateful for the experience. Which would not get very far due to the goals of the parties being incompatible. But eventually, because of the diplomatic virtue of appearing to cooperate, you get a settlement of the matter with international cooperation from foreign partners through projects which complement and support NASA's core development program, of which Spacelab is, indeed, the ur example. While you could get cooperation for experiments to actually land on the Moon with Apollo missions, if you're going to get an "International Apollo" in this mold, its most likely form is in internationally built unmanned lunar scientific missions which contributes to Apollo by furthering the general understanding of the lunar environment.
So shipping a whole ass Titan 2, building a launchpad, and timing the missions, for a ONE TIME flight is somehow practical, you would be better off paying for a flight to get an astronaut on board, which wouldn't happen
I'm not arguing it's practical. And certainly not probable. But if you, as the writer of an allohistorical scenario, want to have a manned Commonwealth mission in a context that isn't too
Ministry of Space-y, the point was merely that there
are ways to do it that do not involve developing an organic manned spaceflight capability. As strange as they may be, the challenge is making it plausible in context, if that's what you're looking for narratively. And you needn't use the actual Gemini 6A/7 mission as a reference point. It can be used as a point of analogizing: The actual spacecraft involved might radically different, as if there's a Commonwealth space program, Gemini as we know it likely butterflied away.
And yes, simply paying for a seat on a flight would be cheaper and simpler. It's also a tack you can take, if you're looking for something less dramatic. Still has its own political issues -- why should NASA sell a seat in the first place? -- but that's a feature, not a bug, as it forces further development of the context for the allohistorical proposition in question.
Frankly, its ridiculous to the point where Kennedy pledging to land on MARS by the end of the decade instead of the moon is more plausible
I mean, that is what McNamara wanted, and it'd give us an excuse to break out the atomic bomb assembly line to feed Ol' Boom-Boom...
Having a LAUNCHER in the 60s is far fetched. a MANNED program and probe program is too far
That there wasn't a launcher was a historical accident, given that both Blue Streak and Black Arrow worked and flew in the Sixties. Having the Commonwealth launch an artificial satellite in the Sixties is a stretch, but only just, as the payloads were there and Black Arrow, with a shoestring budget and prolonged development for it,
did eventually launch a satellite. Having a sustained Commonwealth space program capable of launching a lunar probe in the Sixties is far-fetched. Having a Commonwealth space program that has a manned spacecraft is...yes, I concur, a bridge too far, outside of very narrow circumstances that are engineered to avoid the development of an organic manned spaceflight capability and whose politics may require ASB.
But the discussions of "the Commonwealth space program contributes an unmanned lunar mission to the manned exploration of the Moon" and "bodge together a manned Commonwealth space mission in the Sixties" are two different allohistorical discussions and are incompatible in the same timeline, barring -- as you suggest --
very radical changes whose world is not one we could easily recognize.